Bulldozer tractor



Jan. 22, 1957 c. H. HERR, .JR

BULLDOZER TRACTOR Filed May 5. 1951 4 sheets-sheet J Filed May 5, 1951 c. H. HERR,i JR

BULLDOZER TRACTOR 4 Sheets-Sheet 2 Jan. 22, 1957 Q H, HERR, JR 2,778,131

BULLDOZER TRACTOR Filed May 5, 1951 4 Sheets-Sheet 3 Jan. 22, 1957 C. H. HERR, JR 2,778,131

BULLDOZER TRACTOR Filed May 5, 1951 4 sheets-sheet 4 /0 L 42 /33 /05 /4/ 9 l //'l United States Patent() 2,778,131 BULLDOZER TRACTOR4 Charles H. Herr, Jr., Springfield, Ill., assignor to Allis- Chalmers Manufacturing Company, vMilwaukee, Wis.

Application May 5, 1951, Serial No..224,' 71f7r 6 Claims. (Cl. 37'144) available crawler tractor of general utility type into a 'bulldozer is quite common, and a great numberof attachments have heretofore been suggested for that purpose. Such tween the outside edges of the track belts.

Under certain conditions or special circumstances the width of the bulldozer blade which is necessitated 'by the outside arrangement of the push beams, maybe greater than practical or desirable.

the armed forces; in all of which cases a blade not vmaterially wider than the tread width of the tractor, measured between the outside edges of the track belts, would :be desirable.

In order to take care of special situations such as those mentioned hereinbefore, in which a blade of relatively narice saving 'and economical construction.

Generally, it is an object of the present invention to provide improved equipment for converting an available crawler tractor of general utility type into a material well known three-point suspension principle, that is, to connect the main body and track frames for relative up and down swinging movement on a rearward transverse axis, andfto support the overhanging forward part of the ends don forward portions of `the track frames.

A 'further and important object of the invention is to g Such improved method of conversion, as contemplated by the invention, involves `elimination of the original equalizer b ar and, installation of a substitute mechanism which will menton `the mentioned rearward axis.

A further object of the invention is to provide an improved bulldozer tractor which will be less front heavy and YaEord better v1s1b1l1ty from the operators station than heretofore known bulldozer tractors which are composed of a crawler tractor and conversion attachment of conventional construction.

These and other objects and advantages are attained .by the vpresent invention, various novel features of which will kbe apparent `from the description herein and accom- `partying drawings disclosing an embodiment of the invention, and will be more particularly pointed out in the ap- .pendedclaims In the drawings: f

Fig. 1 is a side view of a bulldozer tractor embodying the invention;

Fig. 2 -is a top View of the bulldozer tractor shown in Fig. l, Fig. 2 including a diagrammatic outline of hydraulic conduits not shown in Fig. l;

Figs. 3 and 4 are views similar to Fig. l and showing the machine in different conditions of adjustment;

Fig, 5 is a somewhat diagrammatic top View of conventional tractor parts shown in Figs. 1 to 4, and of a 'conventional transverse leaf spring which forms .part of the tractor as normally available for general utility purposes but which according to the present invention, is -omitted for conversion purposes as will appear more fully hereinbelow;

4Figs. 6 7 and 8 are side, front and top views, respectively, of the Yforward end of the tractor main body shown in Fig. 5;

Fig. 9 is an enlarged side view of bulldozer parts shown in Fig. l and of parts on the tractor main body to which the bulldozer parts are connected;

Fig. is a top view of the parts shown in Fig. 9;

Fig. 11 is a section on line Xl-Xl ofFig. 10;

Fig. l2 is a section on line XlI-Xll of Fig. 9;

Fig. 13 is a section on line XlII--Xlll of Fig. 9;

Fig. 14 is a detail view of a transverse mounting wing appearing in Fig. 13; and

Figs. to 18, inclusive, are diagrammatic views of a hydraulic system incorporated in the tractor bulldozer as shown in Figs. l and 2.

Referring to Figs. 1 and 2, a tractor main body generally designated by the reference character 1, and a pair of self-laying track units generally designated by the reference characters 2 and 3, respectively, are connected in conventional manner for relative up and down swinging movement on a rearward transverse axis which is indicated in Fig. 2 by the dash-dotted line A-A and which coincides with the axis of rotation of a pair of rear track belt drive sprockets 4 and 6. The tractor main body 1 is of conventional construction and comprises a pair of parallel, transversely spaced side sills or beam elements 7 and 8, and a rearward steering clutch and nal drive housing 9. A tractor engine 11 is located at a forward part of the tractor main body and is mounted in the space between the side sills 7 and 8 in the usual manner. An operators station located on the tractor main body rearwardly of the engine comprises an operators seat 12 with a back rest 13 and arm rests 14. A large fuel tank 16 for the engine is mounted at the rear end of the tractor main body, and an engine radiator and enclosing shell 17 are mounted at the front end of the tractor main body in conformity with well known and generally accepted engineering principles. A bonnet 18 is mounted over the engine 11 on the radiator shell 17 and on a dash panel 19 in the usual manner.

The steering clutch and final drive gear housing 9 encloses the usual mechanism for transmitting power from the engine 11 to the track belt drive sprockets 4 and 6. Such mechanism is generally indicated in dotted lines in Fig. 2, and includes the customary bevel gear drive designated by the reference character 21, a pair of steering clutches designated by the reference characters 22, and two nal drive gear trains designated by the reference characters 23. Fig. 2 also shows the usual steering levers 24, brake pedals 26 and gear shift lever 27 in front of the operators seat 12.

A cross frame member or basket 2S shown in Figs. 1

and 5 extends between the side sills 7 and 8 and forms a conventional part of the tractor main body. Ordinarily, that is, when the tractor is used for general utility purposes, a transverse equalizer spring 29 is pivotally mounted on the basket by means of a longitudinal pivot pin 31, as indicated in Fig. 5. In the tractor bulldozer as shown in Figs. 1 and 2, tractor main body 1 includes the basket 28, but the equalizer spring 29 and the pivot pin 31 are omitted, and a substitute mechanism is provided, as will be more fully explained hereinbelow, for establishing a load transmitting connection between the tractor main body and the track units 2 and 3 forwardly of the axis A-A.

The self-laying track units 2 and 3, like the tractor main body 1, are of conventional construction and are connected with the tractor main body 1 for swinging movement relative to the latter and relative to each other on the axis A-A. As shown in Fig. 5, the self-laying track unit 2 at the left side of the tractor comprises a rigid track frame including outer and inner side channels 32 and 33 and a rearwardly and inwardly extending diagonal brace arm 34. An outboard bearing 36 at the rear end of the side channel 32, and an inboard bearing 37 at the rear end of the diagonal brace arm 34 are aligned on the axis A--A and cooperate with aligned shaft elements 3S and 39, respectively, on the main body to secure the left track frame for up and down swinging movement relative to the tractor main body. A front idler 41 and track rollers, not shown, are mounted on the track frame side channels 32 and 33 for cooperation with an endless track belt 42 in the usual manner.

The foregoing explanations with respect to the selflaying track unit 2 at the left side of the tractor, analogously apply to the self-laying track unit 3 at the right side of the tractor, the terms left and right being used in conformity with the orientation of an operator occupying a forwardly facing position on the seat 12. The reference characters which are applied in Fig. 5 to the self-laying track unit 2 at the left side of the tractor are repeated in the same figure, with primes added, to designate corresponding parts of the self-laying track unit 3 at the right of the tractor.

A material moving tool in the form of a bulldozer is mounted, as generally indicated in Figs. 1 and 2, on the forward part of the tractor main body so as to permit movement of the bulldozer cutting edge into and out of the ground at the forward end of the tractor by downward and upward swinging movements, respectively, of the bulldozer structure in unison with the tractor main body on the axis A-A. ln the condition of the machine as shown in Fig. l, the bulldozer cutting edge is raised a relatively short distance above the ground level which is indicated by the line B-B. Fig. 3 shows the bulldozer and tractor main body swung upwardly on the axis A-A from the position shown in Fig. 2, the bulldozer cutting edge in Fig. 3 being raised to a maximum elevation above the ground level B-B. Fig. 4 shows the bulldozer and tractor main body swung downwardly on the axis A--A from the position shown in Fig. 1, the bulldozer cutting edge in Fig. 4 being lowered to a maximum depth below the ground level B-B.

The details of the bulldozer structure and the connections by means of which the bulldozer structure is rigidly secured to the tractor main body are best illustrated by Figs. 8 to 14. Referring to these figures, and more particularly to Fig. 11, a bulldozer blade 43 of plate metal is bent into the usual arcuate shape to present a concavely curved front face 44 and a convexly curved rear face 46. A cross strip 47 along the lower part of the front face 44 affords a bulldozer cutting edge 48. At the rear of the blade 43, a number of cross members extend longitudinally between the opposite ends of the blade and are welded to the rear face 46 of the latter. One of these cross members presents a vertical wall 49, a horizontal top flange 51 and a forwardly and downwardly'inclined bottom ange 52. A transverse mounting wing 53 which is separately shown in Fig. 14, is connected by welding with the wall 49 at the junction of the latter with the top ange 51, and as shown in Figs. 11 and 13, the mounting wing 53 extends in a vertical plane and upwardly from the top ange 51.

A longitudinal mounting wing S4, best shown in side elevation inv Fig. 9 and in section in Fig. 13, extends in a vertical plane at right angles to the plane of the transverse mounting wing 53, and at the laterally outer side of the main frame side sill 7, as best shown in Figs. 10 and 12. At its forward end the longitudinal mounting wing 54 has a. vertical edge, part of which abuts the wall 49 and another part of which abuts the rear face of the transverse mounting wing 53. Welded seams along the vertical front edge of the longitudinal mounting wing S4 connect the latter with the wall S4 and with the transverse mounting wing 53. As best shown in Fig. 13, the longitudinal mounting wing S4 has a laterally outward extending top ange 56 and a laterally inward extending bottom flange 57, and a triangular gusset plate 58, best shown in Fig. 10, is welded along one edge to the top flange 56 of the Ylongitudinal mounting wing 54 at a forward part of the latter, and another portion of the triangular gusset plate S8is welded` to an edge portion 59 (Fig. 14) of the transverse mounting wing 53, the edge portion 59 extending in a downwardly inclined direction toward,v the left ...end of the At the rear end of the `longitudinal` mounting wing 54, an end plate 63 is secured on edge to the latter so as to extend in a vertical planel and laterallyjoutward from the wing 54,- as shown in Figs. 9 and y12. vThe upperpart of theend plate 63 extends vertically beyond lthe top ange 56 of the wing54, c

mounting wing 5,4 at the rearrend of the latter.

V For the purpose of mounting the bulldozer structure on the tractor main frame,,a bracket` plate 66 issecured 'sill 7 ofthe tractor main body and at a location rearwardly from the vfrontV end of thet-ractor, as-best shown in Fig. l2. The `bracket plate 66-is disposed side sill 7, as shown Another pair of vertically spaced mounting bolts 72 -and through a cross plate 74 at the forward end ofthe tractor main frame, as best `shown in Fig. l1. Referring to Figs. 6, 7 and 8, the cross plate 74 forms part of the wardly and downwardly inclined cross member `76, which also forms part of the normal front end construction of The cross plate 74, cross member 76 and side sills 7 and 3 are rigidly and permanently secured together in conventional manner, as by welding, and -the `entire structure is reinforced by htn'izonftal.,gusset .plates 77 and `by vertical tgusset plates 78, as indicated infFigs-.Yand 8. Y f o l When the tractoris used for general utilitypurposes, 'it issnorrnally equipped with a front bumper, not shown, .and the frontcross plate 74, as normally furnished, has two pairs of vertically. spaced boltholes for mounting the bumper on the tractor mainframe, the left pair of `these vertically spaced bolt -holes beingdesignated in Fig. 7 bythe reference character 79, andthe right lpair beingdesignated by the reference character y81.

` The transverse shown in Fig. l'1,:.extend forward side ofv the 4transholes 79 and S2 and areserve to connect the leftpart A.

foftransverse and longitudinal 1n 1the same figure, yvvith'primes added, to `designate corresponding parts at the right side of the tractor. The right transverse mounting wing 53'- has a pair of Ver- `tica-ily spaced boltl holes, which in the mounted condition of the bulldozer,- regi-ster with 'the vertically spaced bol-t holes Slot the tractor cnossplate 74, shown .in Fig. 7, and longitudinally extending mounting bolts 72 which correspond to the longitudinallyv extending bolts 72 :and 73 'in Fig. ll, extend through the boltholes 81of the tractor cross plate -74 and through the registering bolt holes of 'the transverse mounting wing 53.

`The spaces `between the convex rear -face 46 of the bulldozer blade43 and the `front facesof the transverse mountingwings 53, 53 are closed `by a `channel shaped cover stripy 75 which extends longitudinally of the lblade and isdetachably secured in place by a bolt 8) atl the left end of ithe cover stri y, as shown in Figs. l0, ll and 13, andlby acorrespond-ing bolt, not shown, at the 4right ,end'of the strip-75. As shown in Figs. l0 and 13, It-he left v v bulldozer blade and the front face of the transverse mount-ing wing 53, bracket is permanently secure-d in place by welding. A .correspondingangle bracket, not shown, is provided for the rig-ht end of the cover strip 75.

As pointed out hereinbefore, andas illustrated by Figs. 3 and 4, the Vcutting edge 48 of the bulldozer is Provisions are made to either jprevent or permit unitary pivotal movement of the tractor main body and bulldozer from a bulldozer raised position,k as shown for instance in Fig. 3, toa bulldozer lowered position, as shown for instance in Fig. l4, and vto effect unitary pivotal movement of the tractor 'main body and bulldozer from -a bulldozer lowered to a bulldozer raised position.

disclosed herein top view only, fin'Fig. 2.

,As shown in Figs. l and 2, apair of uprightts 84 and 86 are rigidly mounted on the self-.layingtrack unit 2,

llarly displaced relative to the longitudinal vertical center plane of the track unit 2 so as 'to 'ex-tend obliquely forward toward lthe left side of the tractor main body. A bellorank lever 88 has a fulcrum at 89 on the yoke 87, and a hydraulic jack y'91 for rocking the lever v8-8 on its fulcrum 39 comprises a cylinder 92 which ,ispivote'd aft 93 on the yoke 87, a pis-ton 94 within the cylinder L92,

lever 88, and a ball `and and which angley vof the tractor.

Vwhich is shown in top view in Fig. 2, comprises a hydraulic jack 91 which is a duplicate of the hydraulic jack 91, a bellcrank lever 88' which is a duplicate of the bellcrank lever 88, and =`a supporting structure for the jack 91 and bellcrank lever 88', which is rigidly mounted on the swingable track frame of the right self-layingl track unit 3. The supporting structure for the jack 91' and bellcrank lever 88. comprises uprights 84', 86 and a yoke 87', corresponding, respectively, -to the uprights 84 and 86, and to the yoke 87, but the angular displacement of the yoke 87 is opposite to that of the yoke 87, lthat is, the yoke 87' extends obliquely forward toward the right side of the tractor main body. A stitr link 98' corresponding to the link 98, is connected at its upper end with the bellcrank lever 88 and at its lower end with the bulldozer structure in the same manner as has been explained hereinbefore in connection with the bellcrank lever 88, link 98, and ball and socket joints 99 and 101. Ear plates 103' at the rig-ht end of the bulldozer blade, as shown in Fig. 2, correspond to the ear plates 103 at the left end of the blade, and serve to connect the lower end of the link 98' with the bulldozer structure.

The piston 94 of the hydraulic jack 91 is movable within the cylinder 92 to a rearward limit or bulldozer raised position, as shown 4in Fig. 3, and to a forward limit or bulldozer lowered position, as shown in Fig. 4. The piston of the hydraulic iack 9-1 is similarly movable to bulldozer raisedand bulldozer lowered positions, and in the condition of the machine as shown in Fig. 3 both pistons are in their bulldozer raised positions, While in the condition of the machine as shown in Fig. 4 both pistons lare in their bulldozer lowered positions. The cylinder 92 of the hydraulic jack 91 has a first port 106 at the endat which the piston 94 is located in its bulldozer lowered position (Fig. 4) and the cylinder 92' of the hydraulic jack 91' similarly has a irst port 106 at the end at which the piston of the jack 91' is located in its bulldozer lowered position. Second ports 107 and 107 are formed at the ends of t-he cylinders 92 -and 92', respectively, at which the pistons of the hydraulic jacks are located in their bulldozer raised positions. The iirst ports 106 and 106' are connected with each other by a conduit 108 which has a branch 109 connected with a iirst discharge por-t 111 of a valve mechanism 112 at the right side of the Itractor as shown in Fig. 2. The second cylinder ports 107, 107 are connected with each other by a conduit 113 which has a branch 114 in communication with a second discharge port 116 of the valve mechanism 112.

The conduits 108 and 113 together with their branches 109 and 114, respectively, and the valve mechanism 112 are part of a hydraulic system which is diagrammatically illustrated in various operating conditions by Figs. to 18. Refer-ring to Fig. 15, the hydraulic system is supplied with pressure liuid by a pump P which is driven by the tractor engine 11 in any suitable manner (not shown),.and at its inlet or suction side the pump B draws Ia suitable liquid, such as oil, from a reservoir 117 which is d-i'agrarrlmatically indicated in Fig. l5 and which is shown in Fig. 2 in the foirnI of a tank at the right side The valve mechanism` 112 is' of a well known construction which is commonly used in connection with hydraulically operated tractor bulldozers. As diagrammatically indicated in Fig. l5, :a .rotatable valve bodv 118 and a reciprocable valve body 119 are mounted in a valve housing 121 which, in addition to the mentioned first and second discharge ports 111 and 116, has an inlet port 122 in communication with the discharge side of the pump P, and an outlet port 123 in communication with the reservoir 117. l

Fig. 15 shows the hydraulic system in a hold condition in which the-discharge of the pump-P is directed through the rotatable valve body 118 directly into the outletport 123 and reservoir 117, while escape of tiuid from the forward cylinder spaces 124, 124' is prevented by the reciprocable valve body 119, and escape of pressure iluid from the rearward cylinder spaces 126, 126 is prevented by a `land 127 of the rotatable valve body 118. The pistons 94 and 94 are shown in Fig.v 15 in positions midway of their forward and rearward limit positions, corresponding to the position in which the piston 94 is shown in Fig. 1. In the hold position of the hydraulic system, as shown in Fig. 15, the tractor main body 1 together with the bulldozer structure are prevented from downward swinging movement on the rearward axis `AA and also from upward swinging movement on said axis, but the track units 2 and 3 are capable of controlled swinging movement, in opposite directions, relative to the tractor main body. For instance, the self-laying track unit 2 at the left side of the tractor may swing upward, and as a result pressure uid will be displaced from the forward cylinder space 124 (Fig. 15) ot the jack 91 into the forward cylinder spaoe124' through the conduit 108. As the cylinder 92' of the jack 91' movesv forward, while the cylinder 92 of the jack 91 moves rearward in response to upward swinging movement of the left track unit 2, the track unit 3 at the right side of the tractor will be swung downward on the axis A--A while the track unit 2 at the left side of the tractor swings upward on said axis. Analogou'sly, if the left track unit 2 swings downward, pressure fluid will be displaced from the rearward cylinder space 126 of the jack 91 into the rearward cylinder'space 126 of the jack 91' through the conduit 113, with the result that the right track unit 3 is swung upwardV on the rearward pivot axis A-A relative to the tractor main body 1 while the lett track unit 2 swings downward on saidaxis. In either case, the angular displacement of one track unit form its horizontal position in one direction will be the same as the angular displacement of the other track unit from its horizontal position in the opposite direction. During any transfer of pressure fluid from one of the forward cylinder spaces 124 and 124' to the other, a corresponding transfer of pressure iiuid in the opposite direction will take place between the rearward cylinder spaces 126, 126' through the conduit 113. But there can be no transfer of pressure fluid from either or both of the forward cylinder spaces to one or both of the rearward cylinder spaces as long as the valve mechanism 112 is in the hold condition, in which it is shown in Fig. l5. In other words, in th hold condition of the valve mechanism, the tractor main body and the bulldozer structure are prevented from unitary pivotal movement on the axis A--A in bulldozer lowering direction, and also in bulldozer raising direction.

Fig. 16 shows the hydraulic system in a raise condition in which the discharge of pump P is directed through the rotatable valve body 118 into a passage 128 of the valve housing 121, -and from which passage the pressure tiuid may pass to the discharge port 111 past 4the reciprocable valve body 119. A coil spring 129 normally tends to force the valve body 119 upon its seat, but yields to thepressure of the pump P to let pressure fluid pass from the passage 128 to the discharge port 111 and from the latter throughthe branch conduit 109 and through the conduit 108 into both forward cylinder spaces 124 and 124'. The rearward cylinder spaces 126 and 126 communicate through the conduit 113, branch 114 and through passages 131 and 132 of the valve housing with the outlet port 123, while the valve mechanism the?" is 'in the raised position -as shown in Fig. 16. Admission of l pressure uid simultaneously into beth forward cylinder spaces 124 and 124', as shown in Fig. .16, causes swinging movement af the tractor main body and bulldozer structure in bulldozer raising direction, while pressure huid is being emitted from the rearward cylinder spaces 1-26 and 126', through the conduits 113, 114 into passage 131- and from the latter plast the rotary valve body 118 linto passage 132, outlet 123 and reservoir 117.

Fig. 17 shows the hydraulic system in a lower condition rin which the discharge of the pump -P is directed and 124 through the conduit 108, branch 109, discharge por-t 111 and past thevalve bodyl19 into the passage 12S of the valve housinga-nd from the latter, past the valve body 118 into an internal passage 133 of the val-ve housing, which in turn and prevents `further downward movement of the tractor Application of Huid the cutting edge 48 rests on the ground will tend to'swing the track units 2 and 3 upwardly about the transverse rear force the cutting edge 48 into the ground.

Fig. 18 shows thea-hydraulic systemin a oat condition in `which -the discharge of the pump P is directed 12?, and in which the Vforwardcylixiderspaces 12-4"and 124 and the'rearwardspaces 126 and 126 also communio'ate iwith the outlet port 123 ofA the ivalve body 121. As shown`-i-nPig. -l8,- the Areciprocable'valve body I''is jacks 91 and 91 within the limits of back and forth movement of the pistons 94 and 94 within the cylinders 92 and 92', respectively.

The herein disclosed bulldozer tractor accomplishes That is, it can readily be constructed by converting an existing crawler tractor .10 n'ism whichzeither prenoms unitary/pivotal-movementp the tractor main body and bulldozer from fa .bulldozer It should be yunderstood that it is not intended to limit the invention to the particular form and details described hereinbefore, and Jaat the invention includess'uch other -forms .and ,modifications as areembrac'ed: bythe scope `of the appended claims.

It is ,claimed and vdesired .to secure by Letters Patent:

1. In an excavating machine comprising a crawler tractor and a bulldozer connectedV therewith', the combination" of, a pair of transversely spaced beam elements dozer raised position.

2. In an excavating machine as set forth in claimv l, the combination of a pair of transverse mounting wings extending crosswise of said beam elements and rigidly connected with said bulldozer blade curved rear face of the latter, and means including bolts 11 extending longitudinally of said tractor through said transverse mounting wings for detachably securing said bulldozer to ksaid beam elements. Y

3. In an excavating machine as set forth in claim 1, the combination of a pair of longitudinal mounting wings rigidly connected with said bulldozer blade at said convexly curved rear tace of the latter and in transversely spaced relation to each other so that said longitudinal mounting wings overlap the laterally outer sides, respectively, of said beam elements, brackets secured, respectively, to said beam elements, and means including bolts cooperable with said brackets and with said longitudinal mounting wings for detachably securing said bulldozer to said tractor main body.

4. In an excavating machine as set forth in claim l, the combination of a pair of transverse mounting wings and a pair of longitudinal mounting wings rigidly connected with said bulldozer blade at said convexly curved rear face of the latter, and means including bolts extending longitudinally of said tractor through said transverse mounting Wings, and bolts extending transversely of said tractor through said longitudinal mounting wings, for detachably securing said bulldozer to said beam elements.

5. An excavating tractor comprising in combination: a main frame having a rear inal drive housing and a pair of laterally spaced parallel push beams fixedly secured at their rearward ends to said housing to form a rigid unitary structure; a pair of self-laying track units pivotally connected at their rearward ends to opposite lateral sides, respectively, of said iinal drive housing for independent vertical swinging movement relative to said main frame and each other about a transverse axis, said track units being disposed on laterally outward sides of said push l beams, respectively, in parallel relation to the latter; an engine for driving said track units mounted on forward portions of said push beams in proximate transverse alignment with forward portions of said track units; a bulldozer structure ixedly secured to said push beams for movement therewith, said bulldozer structure including a transversely disposed blade positioned forwardly of and adjacent to said engine and extending laterally in front of said track units; a double acting hydraulic jack at each side of said main frame operatively interposed between the latter and the adjacent track unit for raising and lowering said blade by vertically swinging saidrnain trarne relative to said track units about said transverse axis', and hydraulic pressure means for actuating said jacks including equalizing fluid connections between corresponding ends of said jacks to afford relative vertical swinging movement between said track units without imparting vertical swinging movement to Vsaid main frame, said jacks upon actuation in one direction by said pressure means being operative to swing said main frame downwardly and transfer weight from said track units to said main frame to urge the cutting edge of said blade downwardly into material being excavated.

6. An excavating tractor comprising in combination: a rigid unitary main frame including a final drive housing at the rearward portion of said main frame', a pair of self-laying track units pivotally connected at the rearward end to opposite lateral sides, respectively, of said nal drive housing for independent vertical swinging movement relative to said main frame and each other about a transverse axis, said track units being disposed on laterally outward sides of said main frame respectively; anengine for driving said track units mounted on said main frame forward of said final drive housing; a bulldozer structure iixedly secured to said main frame for movement therewith, said bulldozer structure including a transversely disposed blade positioned forwardly of said engine and extending laterally in front of said track units; a double acting hydraulic jack at each side of said main frame operatively interposed between' the latter and the adjacent track unit for raising and lowering said blade by vertically swinging said main frame relative to said track units about said transverse axis; and a hydraulic pressure means for actuating said jack including equalizing fluid connections between corresponding ends of said jack to afford relative vertical swinging movement between said track units without imparting vertical swinging movement to said main frame, said jacks upon actuation in one direction by said pressure means being operative to swing said main frame downwardly and transfer weight from said track units to said main frame to urge the cutting edge of said blade downwardly into material being excavated.

References Cited in the file of this patent UNITED STATES PATENTS 

